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array-gpio

1.5.2 • Public • Published

array-gpio

array-gpio is a low-level javascript library for Raspberry Pi using direct register control.

It maps the ARM peripheral registers in memory using /dev/mem for PWM, I2C, SPI and /dev/gpiomem for GPIO control.

One of its features is the use of array objects for GPIO input/output control.

It has support for i2c, spi and pwm operations using direct register control.

For IoT or machine-to-machine applications, please check m2m using array-gpio.

ARM Peripheral Support

  • GPIO
  • PWM
  • I2C
  • SPI

Supported Raspberry Pi Devices

  • Model: B+, 2, 3, Zero & Zero W, Compute Module 3, 3B+, 3A+, 4 (generally all 40-pin models)

GPIO pin numbering

This module uses pin numbers based on the physical pin numbers 1~40 from the board header.

Node.js Requirements

  • Node.js version: 8.x, 9.x, 10.x, 11.x, 12.x

Installation

$ npm install array-gpio

Quick Start

Example 1

Create an input/output object and monitor an input

Create an input and output object

// create a raspberry pi object
const r = require('array-gpio');
 
/* Connect a momentary switch button on pin 11 and an led on pin 33 */
 
// set pin 11 as input
let sw = r.setInput(11);
 
// set pin 33 as output
let led = r.setOutput(33);
 
// using .in() and .out() method
 
// set pin 11 as input
let sw = r.in(11);
 
// set pin 33 as output
let led = r.out(33);

Monitor the state of an input object

const r = require('array-gpio');
 
let sw = r.in(11);
let led = r.out(33);
 
/* Pressing the sw button will turn on the led,
   releasing the sw button will turn off the led. */
 
sw.watch((state) => {
  if(state){
    led.on();
  }
  else{
    led.off();
  }
});

Example 2

Using isOn and isOff property

const r = require('array-gpio');
 
let sw = r.in(11);
let led = r.out(33);
 
/* .isOn and .isOff are own properties of input/output objects when they are created
   Check the current state of an input/output object */
 
console.log(sw1.isOn); // false
console.log(led.isOn); // false
 
console.log(sw1.isOff); // true
console.log(led.isOff); // true
 

Example 3

Monitor multiple input pins

const r = require('array-gpio');
 
/* Connect momentary switch buttons on pin 11 and 13 and an led on pin 33 */
 
let sw1 = r.in(11);
let sw2 = r.in(13);
 
let led = r.out(33);
 
/* The .watchInput() method will monitor all inputs.
   The callback argument will be invoked if one of the input's state changes.
   Press the sw1 button to turn on the led, press the sw2 button to turn off the led */
 
r.watchInput(() => {
  if(sw1.isOn){
    led.on();
  }
  else if(sw2.isOn){
    led.off();
  }
});

Example 4

Create an input/output array object

const r = require('array-gpio');
 
/* Connect a momentary switch button for each input pin and an led for each output pin */
 
let inputOption = {pin:[11, 13], index:'pin'};
let outputOption = {pin:[33, 35, 37, 36, 38, 40], index:'pin'};
 
const sw = r.setInput(inputOption);
const led = r.setOutput(outputOption);
 
// turn on the led's sequentially
let LedOn = () => {
  let t = 0;   // initial on time delay in ms
  for(let x in led){
    t += 50;
    led[x].on(t);
  }
}
 
// turn off the led's sequentially
let LedOff = () => {
  let t = 0; // initial off time delay in ms
  for(let x in led){
    t += 50;
    led[x].off(t);
  }
}
 
r.watchInput(() => {
  if(sw[11].isOn){
    LedOn();
  }
  else if(sw[13].isOn){
    LedOff();
  }
});
 

API

Note:

This module uses pin numbering based on the physical pin numbers 1~40 from the board header.

setInput(arg)

or

in(arg)

Sets a GPIO pin or group of GPIO pins as input object.

arg A valid GPIO pin number or an object argument.

Single Object

const r = require('array-gpio');
 
let input = r.setInput(11);
 
// or
 
let input = r.in(11);

Array Object

const r = require('array-gpio');
 
let inputOption = {pin: [11, 13, 15]};
 
const input = r.setInput(inputOption);
 
// or
 
const input = r.in(inputOption);
 
// By default, the array object created is indexed using zero-based indexing
// (indexed from 0 to n-1, where n is the array.length).
 
/* Get the current logical state of each input element */
console.log(input[0].state);
console.log(input[1].state);
console.log(input[2].state);

To use the pin as index, add an index property to the object argument and set the value to 'pin'.

 
let  inputOption = {pin:[11, 13, 15], index: 'pin'};
 
const input = r.setInput(inputOption);
 
/* Get the current logical state of each input element using pin as index */
console.log(input[11].state);
console.log(input[13].state);
console.log(input[15].state);
 
 
/* Iterate over the array object in both cases to access each input element */
for(let x in input){
   console.log(input[x].isOn);
}
 
// or
 
input.forEach(function(value, index){
   console.log(input[index].isOn);
});
 

state

input/output property

Gets the current digital logical state of an input/output object during runtime. It is a getter only property.

Returns true if the object logical state is high or ON.

Returns false if the object logical state is low or OFF.

Example 1
const r = require('array-gpio');
 
let sensor  = r.in(11);
 
// returns the current state of the sensor
console.log(sensor.state); // false
Example 2
const r = require('array-gpio');
 
let sw = r.in(11);
let led = r.out(33);
 
sw.watch(function(){
  if(sw.state && !led.state){
 
  console.log(sw.state); // true
  console.log(led.state); // false
 
  led.on();
 
  console.log(sw.state); // true
  console.log(led.state); // true
  }
});

isOn and isOff

input/output property

Similar with the state property, it will return the current digital logical state of an input/output object with explicit context.

isOn - returns true if the object logical state is high or ON, otherwise it returns false.

isOff - returns true if the object logical state is low or OFF, otherwise it returns false.

Example
const r = require('array-gpio');
 
let sw1 = r.in(11);
let sw2 = r.in(13);
let led = r.out(33);
 
r.watchInput(() => {
  // turns on led if sw1 is on and if led is off
  if(sw1.isOn && led.isOff){
    led.on();
  }
  // turns off led if sw2 is on and if led is on
  else if(sw2.isOn && led.isOn){
    led.off();
  }
});

watch (edge, callback, [s])

input method

Watches the logical state of an input object for changes or state transitions.

edge

1 - watch state changes from low to high (false to true) or rising edge transition

0 - watch state changes from high to low (true to false) or falling edge transition

'both' - watches both state transitions

If edge argument is not provided, it will watch both transitions same as 'both'.

callback

The callback argument will be called asynchronously everytime a state transition is detected based on the above conditions.

You can passed an optional parameters state and pin respectively to the callback argument for any fine-grained application logic execution.

s

This is an an optional scan rate argument in ms (milliseconds). If not provided, scan rate will default to 100 ms, minimum is 1 ms.

A lower value will make your input more responsive but contact bounce will increase. A higher value will make it less responsive but with a lower contact bounce.

Example1
const r = require('array-gpio');
 
let sw = r.in(11);
 
function pinEvent(){
  console.log('pinEvent invoked');
}
 
// pinEvent will be invoked if sw state changes from false to true
sw.watch(1, pinEvent);
 
// pinEvent will be invoked if sw state changes from true to false
sw.watch(0, pinEvent);
 
// edge argument is not provided,
// pinEvent will be invoked if sw state changes from true to false and vice versa
sw.watch(pinEvent);
 
// using a scan rate of 10 ms
sw.watch(pinEvent, 10);
Example 2
const r = require('array-gpio');
 
let sw1 = r.in(11);
let led = r.out(33);
 
// pressing the sw1 button will turn on the led then turns off after 1000 ms delay
// releasing the sw1 button will do nothing
sw1.watch(1, (state) => {
 
  if(state){
    led.on();
    led.off(1000);
  }
 
});

unwatch()

input method

Stops monitoring an input object from the .watch() method.

read([callback])

input/output method

The conventional way of getting the current logical state condition of an input/output object.

Returns logical 1 value if the object state is in high or ON state condition and 0 for low or OFF state condition.

The optional callback parameter will be invoked asynchronously after returning the object state condition.

This method is similar to state property but as a method property, you can use a callback argument to execute any additional application logic based on the object state condition.

Example
const r = require('array-gpio');
 
let sw = r.setInput(11);
let solenoid = r.setOutput(35);
 
sw.read((state) => {
  if(state === 1)
    solenoid.on();
  else
    solenoid.off();  
});

pin

input/output property

Returns the GPIO pin used from any input/output objects.

Example
const r = require('array-gpio');
 
let sw = r.setInput(11);
let led = r.setOutput(33);
 
console.log(sw.pin);  // 11
console.log(led.pin); // 33

close()

input/output method

Closes an input/output object. Removes any events (pin watching) from the object and resets the pin to GPIO input.

Example 1
const r = require('array-gpio');
 
let sw = r.setInput(11);
let led = r.setOutput(33);
 
sw.close();
led.close();
Example 2
const r = require('array-gpio');
 
let input = r.setInput({pin:[11, 13]});
let output = r.setOutput({pin:[33, 35]});
 
function appExitProcess(){
  console.log('closing all I/O objects');
  for(let x in input){
    input[x].close();
  }
  for(let x in output){
    output[x].close();
  }
}
 
// using Ctrl-C for app exit
process.on('SIGINT', function (){
  appExitProcess();
  process.exit(0);
});

setR(value)

input method

Sets the internal resistor of an input pin using either pull up or pull down resistor.

value

'pu' or 1 - Enable internal pull up resistor.

'pd' or 0 - Enable internal pull down resistor.

If argument is not provided, no internal resistor will be used.

Example
const r = require('array-gpio');
 
let sw = r.setInput({pin:[11,13,15]});
 
// using pull up resistor
sw[0].setR('pu');
// using pull down resistor
sw[1].setR(0);
// no internal resistor is used
sw[2].setR();

watchInput(callback, [s])

main module method

Monitor multiple input objects all at once from the main module using .watchInput() method.

It will watch both state transistions from low to high and vice versa for all inputs.

The callback argument is shared by all input objects. It will be invoked asynchronously if any of the input objects changes state.

You can passed an optional parameters - state and pin respectively to the callback argument for any fine-grained application logic execution.

s is an optional scan rate argument in ms (milliseconds). If not provided, scan rate will default to 100 ms, minimum is 1 ms. A lower value will make your input more responsive but contact bounce will increase. A higher value will make it less responsive but with a lower contact bounce.

To capture which input object state has changed, you can use each object's state or isOn property. Or use the pin argument from the callback when it is invoked for any state transitions.

Example 1
const r = require('array-gpio');
 
let sw = r.in({pin:[11, 13, 15], index:'pin'});
let led = r.out({pin:[33, 35], index:'pin'});
 
r.watchInput(() => {
  // if sw[11] is on, led[33] will turn on
  if(sw[11].isOn){
    led[33].on();
  }
  // if sw[13] is on, led[35] will turn on
  else if(sw[13].isOn){
    led[35].on();
  }
  // if sw[15] is on, both led[33] and led[35] will turn off
  else if(sw[15].isOn){
    led[33].off();
    led[35].off();
  }
});
Example 2
const r = require('array-gpio');
 
let sw1 = r.in(11);
let sw2 = r.in(13);
let led = r.out(35);
 
r.watchInput((state, pin) => {
  if(state && sw1.pin === pin){
    led.on();
  }
  else if(state && sw2.pin === pin){
    led.off();
  }
});

unwatchInput()

main module method

Stops monitoring all the input objects from .watchInput() method. It will stop invoking the shared callback argument for any input state changes.

Example
const r = require('array-gpio');
 
let sw1 = r.in(11);
let sw2 = r.in(13);
let sw3 = r.in(15);
 
let led1 = r.out(33);
let led2 = r.out(35);
 
r.watchInput(() => {
  if(sw1.state){
    return led1.on();
  }
  if(sw2.state){
    return led2.on();
  }
  if(sw3.state){
    led1.off();
    led2.off();
  }
});
 
// stops all input pin monitoring after 15 secs
setTimeout(() => r.unwatchInput(), 15000);

setOutput(arg)

or

out(arg)

main module method

Sets a GPIO pin or group of GPIO pins as output object.

arg A valid GPIO pin number or an object argument.

Single Object

const r = require('array-gpio');
 
/* creates a single output object */
let led = r.setOutput(33);
 
// or
 
let led = r.out(33);
 
/* turn on the led */
led.on();

Array Object

const r = require('array-gpio');
 
/* creates an array output object */
let outputOption = {pin:[33, 35, 36]};
 
const output = r.setOutput(outputOption);
 
// or
 
const output = r.out(outputOption);
 
// Similar with input, the array object created is indexed using zero-based indexing
// (indexed from 0 to n-1, where n is the array.length).
 
/* Get the current logical state of each output element */
console.log(output[0].state);
console.log(output[1].state);
console.log(output[2].state);

To use the pin as index, add an index property to the object argument and set the value to 'pin'.

let outputOption = {pin:[33, 35, 36], index:'pin'};
 
const output = r.setOutput(outputOption);
 
/* Get the current logical state of each output element using pin as index */
console.log(output[33].state);
console.log(output[35].state);
console.log(output[36].state);
 
// iterate over the array object in both cases to access each output element
for(let x in output){
   output[x].on();
}
 
// or
 
output.forEach(function(val, index){
   output[index].on();
});

on([t],[callback]) and off([t],[callback])

output method

Sets the state of an output object to logical high state condition (true) or low state condition (false).

t is an optional time delay in milliseconds.

The state will change after the duration of time delay t.

callback

The optional callback argument will be invoked asynchronously after the output state has changed.

You can passed an optional parameter state for any fine-grained application logic execution.

Example
const r = require('array-gpio');
 
let sw1 = r.in(11);
let sw2 = r.in(13);
let actuator1 = r.out(33);
let actuator2 = r.out(35);
 
r.watchInput(() => {
  if(sw1.isOn && actuator1.isOff){
    actuator1.on(200); // turns on after 200 ms delay
    actuator2.on((state) => {
      if(state){
        console.log('actuator2 is on');
      }
    });
  }
  else if(sw2.isOn && actuator2.isOn){
    actuator1.off(50); // turns off after 50 ms delay
    actuator2.off((state) => {
      if(!state){
        console.log('actuator2 is off');
      }
    });
  }
});

write(bit [,callback])

output method

This is the conventional way of setting the ouput state to high or low state condition.

bit - control bit value.

1 or true - high or ON state

0 or false - low or OFF state

callback

The optional callback argument will be invoked asynchronously after the output state has changed.

You can passed an optional parameter state for any fine-grained application logic execution.

Example
const GPIO = require('array-gpio');
 
const sw = GPIO.setInput(11,13);
const motor = GPIO.setOutput(33,35);
 
let sw1 = sw[0];
let sw2 = sw[1];
 
let motorA = motor[0];
let motorB = motor[1];
 
GPIO.watchInput((state) => {
  if(sw1.read()){
    motorA.write(state, () => motorB.write(!state));
  }
  if(sw2.read()){
    motorB.write(state, () => motorA.write(!state));
  }
});

pulse(pw [,callback])

output method

Generates a single square wave pulse with a duration of pw.

pw

This is the pulse width in milliseconds or the time duration of the pulse.

callback

The optional callback argument will be invoked asynchronously when pw time duration expires.

Example
const r = require('array-gpio');
 
let sw1 = r.in(11);
let sw2 = r.in(13);
let actuator = r.out({pin:[33, 35]});
 
r.watchInput(() => {
  // starts a single pulse w/ a duration of 1 sec
  if(sw1.isOn && actuator[0].isOff){
 
    actuator[0].pulse(1000);
 
  }
  // starts a single pulse w/ a duration of 2 secs
  else if(sw2.isOn && actuator[1].isOff){
 
    console.log('start of actuator[1] pulse');
    actuator[1].pulse(3000, () => {
      console.log('end of actuator[1] pulse');
    });
 
  }
});
 

Note: Currently PWM will work on all Raspberry Pi models except on Raspberry Pi 4B model due to firmware issues. Hopefully, it will be fixed in the next latest release of Raspbian OS.

setPWM(pin)

Sets GPIO pins 12 and 33 to alternate function 0 (ALT0) and sets pins 12 and 35 to alternate function 5 (ALT5) for PWM operations.

Creates a pwm object to start PWM to the provided GPIO pin.

This operation requires root access.

pin

Channel 1 - pins 12 and 32.

Channel 2 - pins 33 and 35.

You can only control 2 peripherals independently, one from channel 1 and one from channel 2. If both peripherals are from the same channel, you can control both channels using only the control values (setRange and setData) from one of the peripherals.

setClockFreq(div)

div

The divisor value to calculate the desired clock frequency from a fixed oscillator freq of 19.2 MHz.

(0 to 4095)

freq = 19200000/div

setRange(range)

Sets the period T of the pwm pulse.

range The period T of the pulse

setData(data)

Sets the pw (pulse width) of the pwm pulse.

data The pulse width of the pulse

stop()

Stops temporarily the pulse generation from the system 19.2 MHz clock oscillator.

You can restart the pulse generation at anytime by calling the .pulse() or .setData() method.

close()

Stops PWM operations on the GPIO pin. Resets the pin to GPIO input.

Example 1

/* Connect an led to pin 12. */
 
/* r for raspberry pi */
const r = require('array-gpio');
 
/* create a pwm object using pin 12 */
var pwm = r.setPWM(12);
 
/* set the pwm clock frequency using a div value of 1920 */
pwm.setClockFreq(1920); // sets clock freq to 10kHz or 0.1 ms time resolution for T and pw
 
/* set period (T) of the pulse */
pwm.setRange(1000); // 1000 x 0.1 ms = 100 ms (actual period T)
 
/*
 * set pw (pulse width) of the pulse and start the pulse generation for 2 seconds
 *
 * The led attached to pin 12 should blink for 2 seconds
 */
pwm.setData(100); // 100 x 0.1 ms = 10 ms (actual pw)
 
/* stop the pwm operation and reset pin 12 to GPIO input after 2 secs */
setTimeout(function(){
 
  pwm.stop();
  pwm.close();
 
}, 2000);
 
 

setPWM(pin, freq, T, pw)

Creates a pwm object from a predefined clock frequencies of 10, 100, or 1000 kHz that will provide different time resolutions for the T (period) and pw (pulse width) of your desired pwm pulse.

pin

Choose from channel 1 (12, 32) or channel 2 (33, 35).

freq (kHz)

Choose a predefined clock oscillator frequency of 10, 100, or 1000 kHz

10 kHz provides 0.1 ms resolution

100 kHz provides 0.01 ms resolution

1000 kHz provides 0.001 ms or 1 uS (microsecond) resolution

T (ms)

The initial cycle period of the pulse.

pw (ms)

The initial pulse width of the pulse.

The ratio of pw over T is the pulse duty cycle (pw/T) x 100%.

pulse([pw])

Start the pulse generation or generates a new pulse using the pw argument provided. If pw argument is not provided, it will use the initial pw argument used in .setPWM() constructor and start the pulse generation.

pw (ms) is the pulse width that will be used to generate a new pulse.

You can change the period T of the pulse using the .setRange() and the pulse width pw using .setData() or .pulse() method at anytime in your application.

However in servo motor applications, the period T is usually fixed while changes in pulse width pw controls the rotational position of your servo motors.

Example 2

/* Using a generic micro servo motor (~4.8 to 6.0 V)
 *
 * T = 20 ms (pulse period)
 *
 * pw (pulse width) needed for various servo positions
 *
 * pw 1.0 ms - pos 1, home position
 * pw 1.5 ms - pos 2, rotates 40 degrees cw (clockwise) from pos 1
 * pw 2.0 ms - pos 3, rotates 80 degress cw from pos 1
 * pw 2.5 ms - pos 4, rotates 120 degress cw from pos 1
 *
 */
 
const r = require('array-gpio');
 
var pin  = 33;    /* pin from channel 2 */
var freq = 10;    /* using 10 kHz clock frequency that will provide a 0.1 ms time resolution */
var T    = 200;   /* Use 200 to get the 20 ms period (200 x 0.1 ms = 20 ms) */
var pw   = 10;    /* Use 10 to get an initial pulse width of 1.0 ms (10 x 0.1 ms = 1.0 ms), home position */
 
/* initialize PWM using with above pin, freq, T and pw details */
var pwm = r.setPWM(pin, freq, T, pw);
 
/* create four push buttons sw[0], sw[1], sw[2] and sw[4] */
const sw = r.setInput({pin:[11, 13, 15, 19]});
 
r.watchInput(() => {
  /* Press sw[0] button to rotate the servo motor to pos 1 or home position */
  if(sw[0].isOn){
    pwm.pulse(10);    // 1.0 ms pw
  }
  /* Press sw[1] button to rotate to pos 2 */
  else if(sw[1].isOn){
    pwm.pulse(15);    // 1.5 ms pw
  }
  /* Press sw[2] button to rotate to pos 3 */
  else if(sw[2].isOn){
    pwm.pulse(20);    // 2.0 ms pw
  }
  /* Press sw[3] button to rotate to pos 4 */
  else if(sw[3].isOn){
    pwm.pulse(25);    // 2.5 ms pw
  }
});
 
const appExitProcess = () => {
  console.log('closing all sw and pwm objects');
  for(let x in sw){
    sw[x].close();
  }
  pwm.close();
  process.exit(0);
}
 
process.on('SIGINT', () => {
  console.log('\napp terminated using Ctrl-C');
  appExitProcess();
});
 

setI2C()

Sets i2c pins 03 (SDA) and 05 (SCL) to its alternate function (ALT0) for i2c operation.

Returns an i2c object with properties to configure the I2C interface to start the i2c data transfer operation.

This operation requires root access.

begin()

Starts i2c operation in your application. This operation is integrated in setI2C() method, so there is no need to call it explicitly to start the i2c operation.

end()

Stops i2c operation and resets i2c pins 03 (SDA) and 05 (SCL) to GPIO input pins.

setTransferSpeed(baud)

Sets the i2c clock frequency by converting the baud argument to the equivalent i2c clock divider value.

setClockFreq(div)

Sets the i2c clock speed based on the div divisor value. Check the various div values below and the possible clock speeds that will be generated.

div 2500 => 10us => 100 kHz
div 626  => 2.504us => 399.3610 kHz
div 150  => 60ns => 1.666 MHz (default at reset)
div 148  => 59ns => 1.689 MHz

selectSlave(addr)

Sets the i2c address of the slave device.

addr

The i2c address of the slave device.

write(wbuf, len)

Write a number of bytes to the currently selected i2c slave device.

wbuf The actual data bytes to send/write to the selected i2c slave device.

len The length of bytes or total number of bytes to send/write to the selected i2c slave device.

read(rbuf, len)

Read a number of bytes from the currently selected i2c slave device.

rbuf The actual data bytes to read/receive from the selected i2c slave device.

len The length of bytes or total number of bytes to read/receive from the selected i2c slave device.

Example

/* Using MCP9808 Temperature Sensor
 *   
 * Please read the MCP9808 datasheet on how to configure the chip for more details.
 */
 
const r = require('array-gpio');
 
var i2c = r.setI2C();
 
/* set data transfer speed to 400 kHz */
i2c.setTransferSpeed(400000);
 
/* MCP9808 hardware device address */
let addr = 0x18;
 
/* select the MCP9808 device for data trasfer */
i2c.selectSlave(addr);
 
/* setup the application read and write data buffer */
const wbuf = Buffer.alloc(16); // write buffer
const rbuf = Buffer.alloc(16); // read buffer
 
/* accessing the internal 16-bit manufacturer ID register within MCP9808 */
wbuf[0] = 0x06; // from the MCP9808 datasheet, set the address of the manufacturer ID register to the write buffer
i2c.write(wbuf, 1); // writes 1 data byte to the slave device selecting the MCP9808 manufacturer ID register for data access
 
/* master (rpi) device will now read the content of the 16-bit manufacturer ID register (should be 0x54 as per datasheet) */
/* reading 2 data bytes - the upper byte (rbuf[0]) and lower byte (rbuf[1]) from the manufacturer ID register, ID value is on the lower byte from the datasheet */
i2c.read(rbuf, 2);
 
console.log('MCP9808 ID: ', rbuf[1].toString(16));  // convert the ID value to hex value
 
/* Based on MCP9808 datasheet, compute the temperature data as follows */
function getTemp(){
 
  /* variable for temperature data */
  let Temp;
 
  let UpperByte = rbuf[0];
  let LowerByte = rbuf[1];
 
  UpperByte = UpperByte & 0x1F; // Clear flag bits
 
  /* Temp < 0�C */
  if ((UpperByte & 0x10) == 0x10){
    UpperByte = UpperByte & 0x0F; // Clear SIGN
    Temp = 256 - ((UpperByte * 16) + (LowerByte / 16));
 
  /* Temp > 0�C */
  }else {
    Temp = ((UpperByte * 16) + (LowerByte / 16));
  }
 
  /* Print out temperature data */
  console.log('Temp: ', Temp);
 
}
 
/* get temperature readings every 2 seconds */
setInterval( function(){
  /* accessing the internal 16-bit configuration register within MCP9808
     You can skip accessing this register using default settings */
  wbuf[0] = 0x01; // address of the configuration register
  /* change content of configuration register */
  wbuf[1] = 0x02; // register upper byte, THYST set with +1.5 C
  wbuf[2] = 0x00; // register lower byte (power up defaults)
  i2c.write(wbuf, 3);
 
  /* accessing the internal 16-bit ambient temp register within MCP9808 */
  wbuf[0] = 0x05; // address of ambient temperature register
  i2c.write(wbuf, 1);
 
  /* read the content of ambient temp register */
  i2c.read(rbuf, 2); // read the UpperByte and LowerByte data
 
  /* get temperature data and print out the results */
  getTemp();
 
}, 2000);
 
process.on('SIGINT', function (){
  console.log('\napp terminated using Ctrl-C');
  i2c.end();
  process.exit(0);
});
 

setSPI()

Sets SPI0 bus pins 19 (MOSI), 21 (MISO), 23 (CLK), 24 (CE0) and 26 (CE1) to its alternate function (ALT0) for spi operation.

Returns an spi object with properties to configure the SPI interface.

This operation requires root access.

begin()

Initializes the SPI0 bus pins for spi operation. This process is integrated in setSPI() method, so there is no need to call it explicitly to start the spi operation.

setClockFreq(div)

Sets the SPI clock frequency using a divisor value.

Clock is based on the nominal core clock rate of 250MHz on RPi1 and RPi2, and 400MHz on RPi3.

div

The SPI divisor to generate the SPI clock frequency.

The information below shows the various div value and the clock frequency in kHz that will be generated.

SPI div  2048  = 122.0703125kHz on Rpi2, 195.3125kHz on RPI3
SPI div  1024  = 244.140625kHz on Rpi2, 390.625kHz on RPI3
SPI div  512   = 488.28125kHz on Rpi2, 781.25kHz on RPI3
SPI div  256   = 976.5625kHz on Rpi2, 1.5625MHz on RPI3
SPI div  128   = 1.953125MHz on Rpi2, 3.125MHz on RPI3 (default)
SPI div  64    = 3.90625MHz on Rpi2, 6.250MHz on RPI3
SPI div  32    = 7.8125MHz on Rpi2, 12.5MHz on RPI3
SPI div  16    = 15.625MHz on Rpi2, 25MHz on RPI3
SPI div  8     = 31.25MHz on Rpi2, 50MHz on RPI3

chipSelect(cs)

Sets the chip select pin(s).

When data transfer starts, the selected pin(s) will be asserted or held in active state (usually active low) during data transfer.

cs

Choose from one of cs values below.

cs = 0,  Chip Select 0
cs = 1,  Chip Select 1
cs = 2,  Chip Select 2
cs = 3,  No Chip Select

setCSPolarity(cs, active)

Change the active state of the chip select pin.

cs

The chip select pin you want to change the active state.

active

Select 0 for active low or 1 for active high state.

setDataMode(mode)

Sets the SPI data mode, the clock polariy (CPOL) and phase (CPHA).

mode

Choose from one of SPI mode below.

mode = 0,  CPOL = 0, CPHA = 0
mode = 1,  CPOL = 0, CPHA = 1
mode = 2,  CPOL = 1, CPHA = 0
mode = 3,  CPOL = 1, CPHA = 1

transfer(wbuf, rbuf, len)

Transfers any number of bytes to and from the currently selected spi slave device. This method makes it possible to perform simultaneous write and read operations for date transfer.

Selected CS pins (as previously set by chipSelect) will be held in active state during the data transfer.

wbuf The actual data bytes to send/write to the selected spi slave device.

rbuf The actual data bytes to read/receive from the selected spi slave device.

len The length of bytes or total number of bytes to send/receive from/to the selected spi device.

write(wbuf, len)

Write a number of bytes to the currently selected spi slave chip.

Asserts the currently selected CS pins (as previously set by chipSelect) during the data transfer operations.

wbuf The actual bytes to write/send to the selected spi slave device.

len The length of bytes or total number of bytes to write/send to the selected spi slave device.

read(rbuf, len)

Read a number of bytes from the currently selected spi slave device.

rbuf The actual data bytes to read/receive from the selected spi slave device.

len The length of bytes or total number of bytes to read/receive from the spi slave device.

end()

Stops the SPI data transfer operations. SPI0 pins 19 (MOSI), 21 (MISO), 23 (CLK), 24 (CE0) and 26 (CE1) are reset to GPIO input pins.

Example

/* Using MCP3008 10-bit A/D Converter Chip
 *
 * In this example, we will connect the Vdd and Vref pins to the Raspberry Pi's 3.3 V.
 * Channel 0 (pin 1) will be used for analog input voltage using single-ended mode.
 *
 * Please read the MCP3008 datasheet on how to configure the chip for more details.
 */
 
const r = require('array-gpio');
 
var spi = r.setSPI();
 
spi.setDataMode(0);
spi.setClockFreq(128);
spi.setCSPolarity(0, 0);
spi.chipSelect(0);
 
/* setup write and read data buffer */
const wbuf = Buffer.alloc(16); // write buffer
const rbuf = Buffer.alloc(16); // read buffer
 
/* configure the chip to use CH0 in single-ended mode */
wbuf[0] = 0x01; // start bit
wbuf[1] = 0x80; // using channel 0, single ended
wbuf[2] = 0x00; // don't care data byte as per datasheet
spi.write(wbuf, 3); // write 3 bytes to slave
 
/* alternative way to write and read to a slave at the same time */
//spi.transfer(wbuf, rbuf, 3); // 3 bytes will be sent to slave and 3 bytes to read
 
spi.read(rbuf, 3); // read 3 bytes from slave
/* read A/D conversion result */
/* the 1st byte received through rbuf[0] will be discarded as per datasheet */
var data1 = rbuf[1] << 8;  // 2nd byte, using only 2 bits data
var data2 = rbuf[2];    // 3rd byte, 8 bits data
var value = data1 + data2; // combine both data to create a 10-bit digital output code
 
console.log("* A/D digital output code: ", value);
 
/* compute the output voltage */
var vout = (value * 3.3)/1024;
 
console.log("* A/D voltage output: ", vout);
 
spi.end();

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